1. Field of the Invention
The present invention relates to a distillation apparatus used for carrying out a distillation operation widely employed in a large number of industrial processes, and more particularly, it relates to a distillation apparatus in which heat exchange is effected between a rectifying section and a stripping section.
2. Description of the Related Art
Distillation separation is widely employed in industrial processes in general but is a unit operation that consumes extremely large energy. Therefore, a distillation apparatus in which energy consumption can be reduced has been studied in the industry. In these studies, a heat integrated distillation column (hereinafter sometimes referred to as HIDiC) has been developed as a distillation apparatus excellent in energy saving.
Traditionally, a section located above a feedstock feed stage of a distillation column used for carrying out continuous distillation is referred to as a rectifying section, and a section below the feedstock feed stage is referred to as a stripping section. The distillation column is provided with a condenser for cooling and condensing overhead vapor and a reboiler for heating and boiling a column bottom liquid by heating.
A HIDiC has a basic configuration in which a rectifying section and a stripping section of one distillation column have been separated from each other. The operation pressure of the rectifying section is set to be higher than the operation pressure of the stripping section, so that the operation temperature of the rectifying section becomes higher than the operation temperature of the stripping section. And, the HIDiC is configured so that heat exchange can be effected between the rectifying section and the stripping section. Accordingly, heat is transferred from the rectifying section to the stripping section, and therefore, it is possible to reduce the amount of heat supplied at the reboiler and to reduce the amount of heat removed at the condenser. In other words, by transferring the heat from the rectifying section to the stripping section by the heat exchange, the heat supplied at the reboiler and the heat removed at the condenser can be at least partially substituted, and as a result, a distillation apparatus having extremely high energy efficiency can be obtained.
In order to put such a HIDiC into a practical use, JP H08-66601A has proposed a distillation apparatus, which employs a shell and tube type heat exchange structure as a basic configuration, uses the inside and the outside of a tube respectively as a rectifying section and a stripping section, and can transfer heat from the rectifying section to the stripping section by using a tube wall as a heat transfer surface. Furthermore, as an improvement proposal for this distillation apparatus, JP2004-16928A has proposed a distillation apparatus, which employs a double tube as the tube and uses an innermost portion and a circumferential portion of the double tube respectively as the rectifying section and the stripping section.
Furthermore, International Publication No. WO2011/043199 has proposed a distillation apparatus, in which a rectifying column (a rectifying section) and a stripping column (a stripping section) are connected to each other by way of piping, and heat exchange is effected between the rectifying column and the stripping column by providing a heat exchanger in the rectifying column and introducing a liquid withdrawn from the stripping column into this heat exchanger or by providing a heat exchanger in the stripping column and introducing vapor withdrawn from the rectifying column into this heat exchanger.